1. Field of the Invention
The present invention relates to a movable magnetic head unit such as a magnetic recording/reproducing device with a recording and reproducing function that has means for transmitting a control signal for driving a movable magnetic head.
2. Description of Related Art
FIG. 1 is a partial cutaway vertical sectional view of a rotary drum including an electromagnetically driven type actuator used in a conventional magnetic recording/reproducing device. As shown in FIG. 1, an electromagnetically driven type actuator 21A is fixed to an upper drum 5 with a screw 9, and is rotatable around a rotation axis 3. The rotation axis 3 is supported by bearings 4 fixed to a lower drum 2. A magnetic tape 1, that is, a magnetic recording medium, is obliquely slid along a tape guide (not shown) on the outer surfaces of the upper drum 5 and the lower drum 2.
A magnetic head 6 for recording and reproducing an image signal is adhered to the top of a movable plate disposed on the actuator 21A. The magnetic head 6 can be moved in the direction along the rotation axis 3 in accordance with a control signal. Such a control signal is produced so as to make optimal a signal reproduced at the magnetic head 6, and is transmitted to a slip-ring 8 via a brush 7 to be supplied to the actuator 21A.
In FIG. 1, reference numerals 33 and 34 denote a lower transformer and an upper transformer in a rotary transformer, respectively. The upper transformer 34 is fixed to the upper drum 5 so as to be rotatable around the rotation axis 3. On a surface of the upper transformer 34 opposing the lower transformer 33, a plurality of grooves are formed concentrically with the rotation axis 3, and a coil is provided in each of these grooves. The lower transformer 33 is fixed to the lower drum 2. On a surface of the lower transformer 33 opposing the upper transformer 34, a plurality of grooves are also formed concentrically with the rotation axis 3, and a coil is provided in each of these grooves.
A signal to be recorded on the magnetic tape 1 is sent from the coils in the grooves of the lower transformer 33 to the coils in the grooves of the upper transformer 34 to be supplied to the magnetic head 6. In the reproducing operation, the magnetic head 6 reads a recorded signal from the magnetic tape 1, and the read signal is transmitted by the route reverse of that in the recording operation.
Further, the rotary drum has another similar actuator 21B on the other side of the rotation axis 3 so as to oppose the actuator 21A. These two actuators are controlled as follows:
FIG. 2 is a block diagram showing a conventional magnetic recording/reproducing device having two electromagnetically driven type actuators as above. A first and a second control voltage input terminals 11A and 11B in FIG. 2 are respectively provided with regard to the electromagnetically driven type actuators (i.e., electromechanical transducing elements; hereinafter referred to as the "actuators") 21A and 21B. A first control signal inputted through the first control voltage input terminal 11A is inputted to a first amplifier 19A having a voltage shifting function and is amplified to have a voltage in accordance with the positional change of the actuator 21A. For simplification of the entire system design, the first actuator 21 A is set to be moved, for example by 0 micron when the output voltage of the first amplifier 19A is 0 volt (V).
The output of the first amplifier 19A is inputted to a first power amplifier 20A. The first power amplifier 20A amplifies the voltage of the output signal from the first amplifier 19A at an amplification rate in accordance with a signal inputted through a power amplification control signal terminal 26. The signal outputted from the first power amplifier 20A is supplied to the first actuator 21A via the brush 7 and the slip-ring 8. A second control signal inputted through the second control voltage input terminal 11B is also treated in the similar manner. The description of the treatment of the second control signal is herein omitted, but is apparent from FIG. 2 in which like elements are shown with like reference numerals followed by B instead of A. The output from the first power amplifier 20A or the second power amplifier 20B is selectively outputted to the brush 7 by supplying a switching signal to one of change-over switches 24 through a switching control signal terminal 25.
FIG. 3 shows a sectional view of one of the actuators. Reference numerals 101 and 102 denote cylindrical permanent magnets. A magnetic material referred to as a pole piece 103 is provided between the permanent magnets 101 and 102, thereby forming magnetic fluxes 110 as shown in FIG. 3. The permanent magnets 101 and 102 and the pole piece 103 are surrounded with a hollow cylindrical bobbin 104, which is wound with a coil 105. The cylindrical bobbin 104 is fixed inside of a yoke 108 having a lower flat spring 106 and an upper flat spring 107 therebetween.
A magnetic head 109 is provided at one end of the lower flat spring 106. When a current is allowed to flow through the coil 105 in the counterclockwise direction seen from the above of the drawing, a force to push down the bobbin 104 is generated owing to the interaction with the magnetic fluxes 110, resulting in lowering the magnetic head 109. When a current is allowed to flow in the reverse direction, the magnetic head 109 is raised.
The conventional rotary drum generally has another magnetic head disposed so as to oppose the abovementioned magnetic head. In other words, the rotary drum has another actuator similar to that shown in FIG. 3. As is described referring to FIG. 2 above, the first and the second actuators are controlled by first and second control signals, respectively. The control process of the second actuator 21B is identical to that of the first actuator 21A except that the phase of the second control voltage to be inputted through the second input terminal 11B is shifted at an angle of 180.degree. degrees from that of the first control voltage. The shift between the first control voltage and the second control voltage is caused by the positional differences of the two magnetic heads.
When the aforementioned magnetic recording/reproducing device is used, control signals are supplied to the actuators 21A and 21B, thereby changing the positions of the magnetic heads (shown with the reference numeral 6 in FIG. 1) provided on the actuators 21A and 21B.
In such a conventional magnetic recording/reproducing device, a control signal for driving the actuator is sent to the upper drum by using the brush and the slip-ring as described above. As a result, a fretting noise as well as an electrical noise caused by temporary noncontact between the brush and the slip-ring are generated. Especially in the reproducing operation, such a noise jumps into reproduced signals to cause a white dot noise to appear on a monitoring display. Thus, the quality of the reproduced image is degraded.
In order to solve this problem, the contact pressure between the brush and the slip-ring can be raised so as to reduce the number of noises on the display. This, however, makes the brush wear rapidly, resulting in shortening the useful life of the brush. This method is therefore useful when the brush and the slip-ring can be regularly checked or exchanged, but is nearly impossible to adopt for home appliances which are difficult to be regularly checked. Therefore, it has been desired to develop an inexpensive magnetic head unit of a driving signal transmission system with a high reliability that can be also used for home appliances.